1. Field of the Invention
The present invention relates to a lithographic apparatus and method.
2. Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., comprising part of, one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction.
It is desirable to monitor properties of a radiation beam that is used by the lithographic apparatus to project the pattern from the mask or reticle onto the substrate (e.g., to determine properties of projection system that is used to project the pattern). It is also desirable to be able to monitor alignment of the mask or reticle and the substrate (or a substrate table). Sensors that are used to measure radiation beam properties and to monitor alignment may require the radiation beam to be diffuse in order to allow detection of beam properties or to allow monitoring of alignment with a desired accuracy.
It is desirable to provide, for example, a lithographic apparatus in which diffuse radiation may be generated in a manner that differs from the prior art.